1. Field of the Invention
The present invention relates to a catalyst for synthesizing glycerol carbonate from glycerol, a method for producing the catalyst, and a method for synthesizing glycerol carbonate from glycerol using the catalyst. More specifically, the present invention relates to a catalyst for synthesizing glycerol carbonate from glycerol and urea with high conversion, selectivity and yield, a method for producing the catalyst, and a method for synthesizing glycerol carbonate from glycerol using the catalyst.
2. Description of the Related Art
In recent years, as fossil fuels have become more expensive, biodiesel, along with bioethanol, has attracted attention as a liquid fuel energy source that can replace fossil fuels. Considerable amounts of waste liquids are generated from biodiesel production processes. The waste liquids include a high concentration of glycerol as a by-product and account for about 10% of the biodiesel production. Such by-products containing glycerol may cause secondary pollution. Particularly, a considerable cost is required to treat a large amount of waste glycerol, leading to low economic efficiency of biodiesel production processes. Under these circumstances, there is a need to convert waste glycerol, a by-product of biodiesel production processes, to high value-added glycerol derivatives and to develop new applications of the glycerol derivatives.
Glycerol can be converted to glycerol derivatives, such as glycerol carbonate, 1,3-propanediol, glycolic acid, propylene glycerol, glycidol, propanol and glyceric acid, by chemical/biological methods. Of these, glycerol carbonate (GC, 4-hydroxymethyl-1,3-dioxolan-2-one) is a compound that has biodegradability, low irritability, high boiling point, non-volatility, and moisturizing ability. Glycerol carbonate is a solvent or an intermediate for medical applications and is considered a promising new replacement for propylene carbonate. Glycerol carbonate can also be used as a main component for coatings, paints, detergent additives, vegetable lubricants, lithium battery additives, cosmetic humectants, and gas separation membranes.
For the purpose of increasing the value of glycerol, a great deal of research has been conducted on methods for converting glycerol to glycerol carbonate. Many methods are known for converting glycerol to glycerol carbonate, for example, a method including the reaction of glycerol with a carbonate compound, such as ethylene carbonate or dimethyl carbonate, a method including the reaction of glycerol with carbon dioxide, and a method including the reaction of glycerol with urea. The method including the reaction with a carbonate compound is unfavorable in terms of competitiveness because of the use of the existing carbonate compound, and the method including the reaction with carbon dioxide is environmentally friendly but has the disadvantage of low yield. In contrast, the method including the reaction with cheap inexpensive and environmentally friendly urea as a raw material is receiving much attention due to its high commercial viability.
In methods for synthesizing glycerol carbonate using urea, conversion rate of glycerol, selectivity to glycerol carbonate, and final reaction yield of glycerol carbonate are dependent on reaction catalysts. Thus, there is a need to develop a method for efficiently synthesizing glycerol carbonate using a more highly active reaction catalyst.
In view of this situation, the present inventors have found that a catalyst suitable for the synthesis of glycerol carbonate from glycerol can be produced when an aqueous NaOH solution, an aqueous KOH solution, or a mixture of an aqueous NH4(OH) solution and an aqueous NaOH solution is added to an aqueous solution of a mixture of zinc nitrate and aluminum nitrate, the mixture is aged, the aged mixture is filtered and washed to obtain a solid, and the solid is calcined under an oxygen, nitrogen or helium atmosphere. The present inventors have also found that the use of the catalyst enables the synthesis of glycerol carbonate from glycerol and urea with high conversion, selectivity and yield. Based on these findings, the present invention has been accomplished.